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A fuse can clear a fault within a quarter cycle of the fault current, while a circuit breaker may take around half to one cycle to clear the fault. The response time of a fuse can be as fast as 0.002 seconds, whereas a circuit breaker typically responds in the range of 0.02 to 0.05 seconds.
Circuit breakers and fuses disconnect when current exceeds a predetermined safe level. However they cannot sense other critical faults, such as unbalanced currents—for example, when a transformer winding contacts ground. By themselves, circuit breakers and fuses cannot distinguish between short circuits and high levels of electrical demand.
Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate. Time overcurrent protection operates based on a current vs time curve. Based on this curve, if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate.
The utilization categories category for low-voltage switchgear defines the characteristic operating conditions for switchgear such as contactors, circuit-breakers, circuit-breaker-fuse units, contactor relays, etc. These devices are dimensioned for different electrical loads and for different operating conditions.
Circuit breakers with higher ratings can have adjustable trip settings, allowing fewer standardized products to be used, adjusted to the applicable precise ratings when installed. For example, a circuit breaker with a 400 ampere frame size might have its over-current detection threshold set only 300 amperes where that rating is appropriate.
Fuse – over-current protection, one time use; Circuit breaker – resettable fuse in the form of a mechanical switch; Resettable fuse or PolySwitch – circuit breaker action using solid state device; Ground-fault protection or residual-current device – circuit breaker sensitive to mains currents passing to ground
In electrical engineering, IEC 60269 is a set of technical standards for low-voltage power fuses. [1] The standard is in four volumes, which describe general requirements, fuses for industrial and commercial applications, fuses for residential applications, and fuses to protect semiconductor devices.
Fuses, circuit breakers, and current limiters are commonly used overcurrent protection (OCP) mechanisms to control the risks. Circuit breakers, relays, and fuses protect circuit wiring from damage caused by overcurrent.